Poster of the Sulawesi, Indonesia Earthquake of 16 November 2008 - Magnitude 7.4

Tectonic Summary

The Sulawesi, Indonesia earthquake of November 16, 2008
occurred as a result of thrust faulting on a plate-boundary that is marked
by the North Sulawesi trench, separating the Celebes Sea basin and the
Minahassa peninsula. Eastern Indonesia is characterized by complex
tectonics in which motions of numerous small plates are accommodating
large-scale convergence between the Australia and Eurasia plates. At the
location of today's earthquake, the Celebes Sea basin (commonly considered
part of the Sunda plate) moves south with respect to the Minahassa
peninsula (part of the Molucca Sea plate) at a velocity of about 30
mm/year. The lithosphere of the Celebes Sea basin is thrust beneath that
of the Minahassa peninsula and is seismically active to a depth of about
250 km.

The earthquake occurred approximately 25 km off the northern coast of the
Minahassa peninsula of the Island of Sulawesi in an area that has seen
large earthquakes in the past. For example, a damaging magnitude 7.6
earthquake occurred on April 18, 1990 approximately 85 km east of today's
earthquake. The magnitude 7.6 earthquake in 1990 was followed a year later
by a magnitude 7.5 earthquake in approximately the same place. More
recently a magnitude 7.0 occurred within 45 km of today's earthquake on
November 25, 1997. The 1997 earthquake caused damage to at least 90
building in the Gorontalo area of northern Sulawesi.

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